Fork safety means for clocks with pallet escapement



p 1956 H. HETTICH 2,763,123

FORK SAFETY MEANS FOR CLOCKS WITH PALLET ESCAPEMENT Filed Jan. 25. 1954 Camus M United States ?atent G FORK SAFETY MEANS FOR CLOCKS WITH PALLET ESCAPEMENT Hugo Hettich, Ludwigshafen am Boden See, Germany Application January 25, 1954, Serial No. 405,970

Claims priority, application Germany January 26, 1953 4 Claims. (Cl. 58-117) This invention relates to clocks with balance wheel and pallet controlled operation and more particularly to safety means for the pallet fork of such type of clocks.

In clocks of the type mentioned a driving impulse is transmitted by the pallet fork to the drive pin carried by the balance wheel each time a reciprocating movement of the pallet takes place. In the outer portions of the oscillatory movement of the balance wheel within the supplementary arcs the drive pin completely leaves the fork but is required to enter it again on its reverse swinging movcment. it will be understood therefore that during the movement of the drive pin within the supplementary arcs the fork positively must be held in the position in which it was left by the pin. In this position in which the fork is abutting against one of its limiting pins it is held due to the action of the pressure angle of the tooth flank of the escape wheel, this holding force being, however, so subtile that under certain circumstances such as due to a shock it will fail in its function so that the fork will swing out of the position in which it is capable of receiving the reversely swinging drive pin of the balance wheel assembly so that the drive pin will engage the fork horn externally thereby stalling the clock.

in order to prevent such occurrence fork safety means have been designed.

Fork safety means are known which in general are satisfactory in operation, but have the drawback that the fork horns have to be very long so as to enter into the range of movement of the drive pin. This requires the guidance angle i. e. the angular path of the balance wheel assembly during which the fork is in engagement with the drive pins to be very large. A large guidance angle (angular path), however, is less convenient for correct operation of the clock than a small guidance angle.

Fork safety means providing a small angular path and using a safety roller have also been proposed which, however, have the disadvantage that there is a comparatively small intersection between the peripheral circle of the safety roller and the oscillatory circuit of the safety pin carried by the pallet and cooperating with the safety roller, so that the various parts require very high precision in manufacture and assembly thus increasing the cost of production.

The present invention has for its object the provision of fork safety means providing even with a small angular path an intersection suflicient even with less high accuracy in the manufacture of the parts to assure a reliable localization of the fork.

This and other objects and advantages of the invention will be apparent from the following description and the accompanying drawing showing some embodiments thereof. In the drawing:

Fig. l is a side elevation of a balance wheel having an upright staif and embodying an escapement mechanism and fork safety means in accordance with one form of the invention;

Fig. 2 is a horizontal sectional view along line II-II of Fig. 1;

Fig. 3 is a fragmentary view of a modification of the fork safety means;

Fig. 4 is a sectional view along line IV-IV of Fig. 3.

Referring first to the embodiment illustrated in Figs. i and 2, which show a balance wheel mounted on an upright staff together with its associated escapement mechanism as component parts of a clockwork (not illustrated) such as a wall clock. This clockwork comprises a pair of plates 1 and 2 between which an arbor 4 carrying an escape wheel 3 and a shaft 6 carrying a pallet 5 are mounted. The shaft 6 further carries rigidly secured thereto in a manner known as such a pallet fork 7 having horns 7 and 7 bent at right angles thereto and cooperating with drive pins 9 secured to the balance wheel 8 (Fig. 2).

The horn 7" has its end extended and bent at right angles thus forming a safety pin 7" extending in parallel relationship with the balance wheel staff 11 and cooperating with an annular safety member 10. This annular safety member which constitutes a special feature of the invention is arranged to surround the balance wheel staff ii and is rigidly connected to the balance wheel assembly. in the embodiment shown this connection is provided by a pair of drive pins 8 in turn secured to the spoke arm 3' indicated in Pig. 2 of the balance wheel 8.

The annular safety member it) is so arranged with relation to the pallet fork that the extended horn 7" is projecting through the plane of the annular safety member if this latter eing in addition provided as shown in Fig. 2 with a slot or recess 12 which is so located and dimensioned that while the pallet fork is performing its oscillatory movements, the fork horns 7 and "i" are reciprocating between an innermost position shown in Fig. 2 with full lines and an outermost position shown in the same figure with dash-dotted lines during which reciprocating motion the axially bent end 7 is entering and leaving respectively the slot 12 of the annular member 10. As will be noted alternately the inner periphery or the outer periphery of the annular safety member 18 is acting as an abutment face locating the fork in its correct position during the oscillatory movement of the balance wheel.

As to the balance wheel assembly any suitable design and mounting may be provided as described by way of example in my co-pending U. S. application Serial No. 342,893 filed March 17, 1953, now Patent 2,728,188, issued December 27, 1955.

As shown in Figures 1 and 2 the plate 2 has secured thereto by means of screws 13 an angular bracket 14 through the bore 15' of which, a guiding wire 17 clamped to an upper lateral arm 14 of the bracket depends vertically downward is guided through a bore 18 in a lower lateral arm 14 of the bracket and is secured thereto by means of a screw 19. A coiled balance wheel spring 20 is secured with its upper end to the lateral arm 14' of the angular bracket 14 while its lower end is attached to the hollow spindle or staff 11 which in turn carries the balance wheel 3 so that the balance wheel assembly 3, 11 is rotatably suspended from the spring 2%. The coil spring 28 consists of two parts 20, 20" of the same number of windings but wound in opposite direction so that the spring suspended balance wheel assembly is prevented from swinging vertically up and down during its horizontal oscillatory movement.

In the embodiment shown in Fig. 3 a cup-shaped member 21 is substituted for the annular safety member iii) and secured to the balance wheel staff 11. As shown in Fig. 4' this cup-shaped member is formed at a suitable location of its cylindrical wall with a slot 22 corresponding to the slot 12 of the annular safety member 18 shown in Figs 1 and 2, so that the bent fork end 7 will enter or leave the slot 22 during the reciprocating movement of fork 7 in the same manner as described in connection with the embodiment shown in Figs. 1 and 2.

It will be apparent from the foregoing that the invention provides even with a small guidance angle i. e. with a small angular path of the balance wheel assembly during which the fork is in engagement with the drive pins a comparatively ample intersection between the peripheral circle of the annular safety member and the oscillatory circuit of the safety pin, so that reliable localization of the fork is assured without it being necessary to take care for a high accuracy in the manufacture of the various parts of the escapement mechanism.

What is claimed is: v 1. In a clockwork, a spring-driven escape Wheel and a pallet cooperating therewith, a pallet fork positively to pass through said gap and to abut alternately the inner and the outer periphery of said safety member thereby assuring correct position of said pallet fork during each oscillation of the balance wheel assembly.

2. In a clockwork, a structure as defined in claim 1, wherein a pair of drive pins is rigidly secured to said balance wheel assembly.

3. In clockwork, a structure as defined in claim 1 wherein said pallet fork is located between said balance Wheel and said ring, said drive pins at one end being secured to a spoke arm of the balance wheel and at the other end supporting said ring.

4. In clockwork, a structure as defined in claim 2 wherein said pallet fork is located between said balance wheel and said ring, said drive pins at one end being secured to a spoke arm of the balance wheel and at the other end supporting said ring.

References Cited in the file of this patent FOREIGN PATENTS 377,263 France July 5, 1907 565,454 Germany Dec. 1, 1932 793,267 France Nov. 16, 1935 536,600 Great Britain May 21, 1941 

